U.S. patent number 4,228,327 [Application Number 06/014,301] was granted by the patent office on 1980-10-14 for electromagnetic type acoustic transducers.
Invention is credited to Tadashi Sawafuji.
United States Patent |
4,228,327 |
Sawafuji |
October 14, 1980 |
Electromagnetic type acoustic transducers
Abstract
An electromagnetic type acoustic transducer comprises a
vibratable diaphragm including a conductor and disposed within a
magnetic field defined by a permanent magnet. Support members which
are expandable and contractible in the direction at right angles
with the diaphragm are fixed to both surfaces of the diaphragm. A
frame is provided for fixing the support members such that the
expansion and contraction thereof is not prevented. The support
members may be folded and formed to a bellows-like state. Use is
also made of a conductor forming spiral convolutions. The permanent
magnet is disposed and retained at a vibration gap with respect to
the diaphragm.
Inventors: |
Sawafuji; Tadashi (Toshima-ku,
Tokyo, JP) |
Family
ID: |
12096367 |
Appl.
No.: |
06/014,301 |
Filed: |
February 23, 1979 |
Foreign Application Priority Data
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Feb 25, 1978 [JP] |
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53-22931[U] |
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Current U.S.
Class: |
381/398; 381/408;
381/431 |
Current CPC
Class: |
H04R
7/20 (20130101); H04R 9/047 (20130101) |
Current International
Class: |
H04R
9/04 (20060101); H04R 7/20 (20060101); H04R
7/00 (20060101); H04R 9/00 (20060101); H04R
007/18 (); H04R 009/02 () |
Field of
Search: |
;179/115.5PV,115.5ES,115.5R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cook; Daryl W.
Attorney, Agent or Firm: Cantor and Singer
Claims
What is claimed is:
1. An electromagnetic type acoustic transducer comprising a
vibratable diaphragm including a conductor and disposed within a
magnetic field defined by a permanent magent, support members which
are expandable and contractible in the direction at right angles
with said diaphragm and are fixed to both surfaces thereof, and a
frame to which said support members are fixed such that the
expansion and contraction thereof are not prevented.
2. An electromagnetic type acoustic transducer as claimed in claim
1, in which said support members are folded and formed to a
bellows-like state.
3. An electromagnetic type acoustic transducer as claimed in claim
2, in which said support members are formed of Japanese paper,
cloth or unwoven fabric of the order of 0.01 to 0.07 mm thickness
which is impregnated with silicon rubber paint, or a metallic
titanium thin plate of the order of 0.01 to 0.05 mm thickness.
4. An electromagnetic type acoustic transducer as claimed in claim
1, in which a conductor defining spiral convolutions is formed on
said diaphragm, and a permanent magnet is retained at a vibration
gap with respect to said diaphragm.
5. An electromagnetic type acoustic transducer as claimed in claim
1, in which a conductor is formed on a rectangular diaphragm is
zigzag relation which is, in turn, folded such that said conductor
provides root portions with its intermediate portions providing
crest portions, and permanent magnets in the form of triangular
rods are disposed on the inner faces of the crest portions and
retained at a vibration gap with respect to said diaphragm.
Description
BACKGROUND OF THE INVENTION
The present invention relates to improvements in acoustic
transducers of the electromagnetic type including plane-driving
type diaphragms, which are intended for use in loudspeakers,
earphones, head phones or mocrophones.
For example, an acoustic transducer of the electromagnetic type
that includes a vibratable diaphragm having a conductor and
disposed within a magnetic field defined by a permanent magnet is
described in U.S. Pat. No. 3,919,498 specification. In the
transducer of this type, since the diaphragm is secured through a
suitable fixing member to the magnet which faces it at its entire
peripheral edge and its center, the entire peripheral edge and the
center undergo no vibration so that the diaphragm is not
plane-driven. Consequently, the transducer of this type is
disadvantageous in that the amplitude of the diaphragm is small,
resulting in unfaithful reproduction of a low sound range and that
the allowable input cannot be raised. The present invention
provides an electromagnetic type acoustic transducer which avoids
these and other drawbacks.
SUMMARY OF THE INVENTION
According to the present invention there is provided an
electromagnetic type acoustic transducer including a vibratatable
diaphragm having a conductor and disposed within a magnetic field
defined by a permanent magnet. The diaphragm is fixedly provided on
both surfaces of its entire peripheral edge with expandable and
retractible support members which are, in turn, secured to a frame.
The expandable and restorable properties of this diaphragm leads to
an increase in the amplitude thereof and makes it possible to
plane-drive it in the same phase over its entire surface. In
particular, it is possible to faithfully reproduce a low sound
range and increase the allowable input.
The above and other features and advantages will be clear from the
following detailed description of exemplary preferred embodiments
illustrated in the appended drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view, partially cut away, of the
electromagnetic type acoustic transducer intended for use in head
phones according to the present invention, which is enlarged on
about two-fold scale and in which the conductor is shown to be
partially omitted;
FIG. 2 is a sectional view taken along the line I--I of FIG. 1;
FIG. 3 is a perspective view, partially cut away, of other
electromagnetic type acoustic transducer modified for use in head
phones according to the present invention, which is enlarged on an
about two-fold scale and in which the conductor is shown to be
partially omitted;
FIG. 4 is a sectional view taken along the line II--II of FIG.
3;
FIG. 5 is a perspective view of a sound generating element for
other electromagnetic type acoustic transducer intended for use in
loudspeakers according to the present invention;
FIG. 6 is a plane view of a diaphragm for other electromagnetic
type acoustic transducer designed for use in loudspeakers in
accordance with the present invention; and
FIG. 7 is a perspective view of the sound generating element to
which the diaphragm of FIG. 6 is applied.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be explained in greater detail with
reference to the drawing. FIGS. 1 and 2 generally show a square
electromagnetic type acoustic transducer 10 intended for use in
head phones. A sound generating element is a flat and square
diaphragm 11 which is provided on its upper surface with a square,
continuous conductor 12 forming spiral convolutions. The conductor
12 is composed of an aluminium foil of a thickness of about 0.01 mm
bonded to a film of about 0.01 to 0.1 mm thickness and made of
synthetic resin whose flexibility and rigidity are not
substantially affected by changes in room and ambient temperatures,
such as polyester, polyethylene, polypropylene or nylon, or a
square thin film of about 0.01 to 0.05 mm thickness and made of a
non-magnetic metal foil such as titanium or aluminium foil on the
conductor-forming surface of which is laminated an insulating thin
layer, followed by etching of said aluminium foil. The conductor 12
is also provided at its peripheral edge 13 with a terminal 14, and
a back conductor 16 connected electrically to conductor 12 at the
center portion 15 of diaphragm 11 is provided at its other end with
a terminal 17.
To both surfaces of the entire peripheral edge 18 of diaphragm 11
are firmly bonded tongue pieces 19a of bellows-like support members
19 each having a M-shaped configuration in section by means of a
suitable strong bonding agent, and to the inside of frame 20 are
firmly bonded other tongue pieces 19b of the support members 19 by
means of a suitable strong bonding agent. In this way, the
diaphragm 11 is supported to frame 20 by the support members 19 in
suspension fashion. As the material for the support members 19, use
may be made of Japanese paper, cloth or unwoven fabric of the other
of about 0.01 to 0.07 mm thickness which is impregnated with
silicon rubber paint, or a metallic titanium thin plate of the
order of 0.01 to 0.05 mm thickness since they excel in durability
and restorable and working properties.
A lower portion of frame 20 is formed integrally with a bottom
plate 22 having a number of peripheral perforations. Alternatively,
such a bottom plate 22 may be fixed thereto by means of screws. The
bottom plate 22 is magnetized in such a manner that it has a north
pole at the center 23 and an annular south pole at the periphery
24. A permanent magnet plate 26 of ferrite defining an annular
non-magnetized region is secured to a portion between the north and
south poles by suitable bonding means such as screws or strong
adhesives. A vibration gap 27 between the diaphragm 11 and the
upper face of the permanent magnet plate 26 is such that the
diaphragm 11 does not come in contact with the plate 26 at the
maximum amplitude of diaphragm 11.
When sound current flows through the conductor 12 of diaphragm 11,
the diaphragm 11 vibrates over its entire surface according to the
Fleming's rule to reproduce a sound. Since the upper and lower
portions of the entire peripheral edge of diaphragm 11 is supported
by the support members 19 constructed as aforesaid, the diaphragm
can well vibrate with a larger amplitude by the expanding and
contracting action of the bellows of the support members, resulting
in faithful reproduction of a low sound range and an increase in
the allowable input.
A sound generating element for other electromagnetic type acoustic
transducer 30 shown in FIGS. 3 and 4 and designed for use in head
phones is a flat, circular diaphragm 31 which is provided on its
upper surface with a continuous conductor 32 forming circularly
spiral convolutions, which is bonded to a circular thin film of the
same material as the diaphragm 11. The conductor 32 is provided at
its peripheral portion 33 with a terminal 34, and a back conductor
36 connected electrically to the conductor 32 at the center portion
35 is provided at its other end with another terminal 37.
To both surfaces of the entire peripheral edge 38 of diaphragm 31
are firmly bonded by means of a suitable strong bonding agent
tongue pieces 39a of bellows-like circular support members 39 which
are formed of the same material as the aforesaid support members 19
and have a M-shaped configuration in section. Other tongue pieces
39b are firmly bonded by means of a suitable strong bonding agent
to annular plates 40a and 40b which are fixed by screws or other
suitable fixing means to the upper and lower portions of a circular
frame 40. In this way, the diaphragm 31 is supported to the frame
40 by the support members 39 in suspension fashion.
In view of its production the circular support members comprises at
least four pieces which are to be arranged in a circle to the
circular support members.
The lower annular plate 40b of the frame 40 is provided at its
lower portion with a circular bottom plate 42 having perforations
41 in the same manner as in the aforesaid bottom plate 22. The
bottom plate 42 is magnetized in such a manner that it has a north
pole at the center 43 and an annular south pole at the periphery
44. A permanent magnet plate 46 of ferrite forming a non-magnetized
region is fixed provided to a portion between the north and south
poles. A vibration gap 47 between the diaphragm 31 and the upper
surface of the permanent magnet plate 46 of ferrite is such that
the diaphragm 31 does not come in contact with the permanent magnet
plate 46 at the maximum amplitude of diaphragm 31.
The action and effect of the sound generating element of this type
are similar to those of the sound generating element of the
aforesaid type.
In the electromagnetic type acoustic tranducers 10 and 30
illustrated in FIGS. 1 to 4, the respective support members 19 and
39 have a M-shaped configuration in section and a single folded
portion, but they may have a plurality of folded portions extending
in opposite directions with each other. On the other hand, the
conductors 12 and 32 of the sound generating elements are formed on
one sides of the thin films, while the permanent magnet plates 26
and 46 are disposed one sides of diaphragms 11 and 31. However,
conductors may be formed on both sides of a thin film, which are
connected to each other at the center of a diaphragm.
Alternatively, permanent plates may be disposed on both sides of a
diaphragm. When the permanent magnet plates are provided on both
sides of the diaphragm, it is required to form a number of
perforations in the central annular non-magnetized portion of each
permanent magnet plate.
As shown in FIG. 5, a sound generating element for further
electromagnetic type acoustic transducer intended for use in
loudspeakers in accordance with the present invention is a square,
bellows-like diaphragm 51. This diaphragm 51 is formed by folding a
thin film of the same material as the foregoing diaphragm 11 such
that projecting portions with a triangular configuration in section
are successively formed. The respective roots of the bellows of
diaphragm 51 are provided with a conductor 52 in zigzag relation
and in series therewith. The conductor 52 is then caused to conduct
sound currents in alternate directions.
To both sides of diaphragm 51 at right angles with the bellows are
firmly bonded support rods 68 such that they are flush with the
periphery 58 of diaphragm 51. Each support rod 68 is of a 7-shaped
configuration in section, and is formed of aluminium or metallic
tiranium. This rod is also of light weight and undergoes no
deformation due to the vibrations of diaphragm 51. The periphery 58
and the support rods 68 are supported to a frame in suspension
fashion by means of support members which are similar to the
support members 19 as shown in FIGS. 1 and 2. The diaphragm 51 is
provided at its back with ferrite-made permanent magnets 66 in the
form of triangular rods which set up magnetic fluxes at right
angles with the conductor 52 arranged on the roots. Numeral 67 here
denotes a vibration gap. When a plurality of conductors 52 are
arranged on each root in such a manner that they are caused to
conduct sound currents in the same direction, a larger output is
obtained which is suitable for use in loudspeakers.
As shown in FIGS. 6 and 7, a sound generating element for still
further electromagnetic type acoustic transducer indended for use
in loudspeakers is a square, bellows-like diaphragm 71. A
corrugated conductor 72 is formed on a rectangular thin film formed
of the same material as the thin film forming the diaphragm 11
shown in FIGS. 1 and 2 by known printing means. This conductor 72
is then folded such that the longitudinal conductor 72 provides
root portions and the intermediate portions of the root portions
provide crest portions, whereby projecting portions with a
triangular configuration in section are sucessively formed.
To both sides of diaphragm 71 at right angles with the bellows are
firmly bonded support rods 88 similar to the support rods 68 as
shown in FIG. 5 in such a manner that they are flush with the
periphery 78 of diaphragm 71. The periphery 78 and the support rods
88 are supported to a frame in suspension fashion by means of
support members similar to the support members 19 shown in FIGS. 1
and 2. The diaphragm 71 is provided at its back with ferrite-made
permanent magnets 86 which cause magnetic fluxes at right angles
with a conductor 72 arranged on the root portions. The diaphragm 71
is also provided at its back with a conductor similar to conductor
72 with one ends of both conductors being connected to each other.
Thus each root is provided at its surface and back with two
conductors. When the conductors at the same root portion are caused
to conduct sound currents in the same direction, a larger output is
obtained which is suitable for use in loudspeakers.
The configuration of the diaphragms and permanent magnets for the
sound generating elements used in the present invention is not
limited to that illustrated. In other words, the diaphragm may be
flat as a whole and may have at its peripheral edge a plane portion
to which support members are mounted.
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